Map Your Neighborhood, by the Numbers

A new Web site allows home buyers, real-estate developers, nonprofit groups and any other interested parties to map neighborhoods for free using a wide range of data, such as per-capita income, education levels and unemployment. PolicyMap is a clever tool that makes government statistics more useful and accessible, though it also highlights some limitations in the U.S.’s numerical self-knowledge.

A part of a PolicyMap of percentage of residents with bachelor’s degrees in 2000, in Sen. Barack Obama’s Chicago neighborhood (his home is marked with an X). The darker shading indicates a higher percentage of residents graduated college. Dark purple means more than 22.94% of residents have bachelor’s degrees.

PolicyMap was created by The Reinvestment Fund, a Philadelphia-based organization that finances urban development. The group found that it needed mapping tools to help it choose neighborhoods for investment, and also to help investors track their projects in the context of neighborhood characteristics rather than through unenlightening pie charts. “We want to be able to get good data into the hands of people who are making public-policy decisions,” Maggie McCullough, director of PolicyMap, told me.

The internal mapping project launched as a public tool in May, sharing for free all data PolicyMap gets for free, mostly from the federal government — roughly 80% of the 4,000 indicators PolicyMap says it provides. The rest of the indicators, including projections bringing older federal data up to date, are available only to subscribers, of which the site had fewer than 200 as of last week, according to Ms. McCullough.

Free users can access a wide range of data, and the site is easy to use and explains fully its sources — and its data’s limitations. These include age — many of the numbers come from the 2000 Census — and low resolution of some indicators, which are available only on the county or state level, not block by block. For instance, the Energy Information Administration reports residential electricity usage only by state. Crime data are also spotty, though PolicyMap will be adding city-level numbers in the coming weeks. “So many people are interested in the crime data but it’s probably the hardest to map nationally,” Ms. McCullough said. (Relying on reports from users and the news media, UCrime maps crime at and near select universities, and SpotCrime maps some neighborhoods.)

PolicyMap is heavy on housing data because of its creator’s mission, but it is adding a broader range of numbers. Coming soon: health data by county from the Centers for Disease Control and Prevention, such as infant mortality and Medicare enrollees. The site also recently added campaign contributions.

One data point you won’t see is foreclosure rates, a stat I wrote about recently. That’s because Ms. McCullough isn’t comfortable with the numbers available — she’s compared them with numbers acquired directly from clerks, and found them to be quite different.

About The Numbers

The Wall Street Journal examines numbers in the news, business and politics. Some numbers are flat-out wrong or biased, while others are valid and help us make informed decisions. We tell the stories behind the stats in occasional updates on this blog.